This topic should better have been opened in the Wireless section rather than security ...
The 2 antennas never transmit at the same time. The one giving the best signal is used to receive and it's that same antenna used to transmit back to client. So they are used alternatively and the power sent through each one is then of course the same.
the only thing you can do is declare if you will use both or only one. Only one is giving worse results obviously.
Best regards,
Nicolas
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